At first glance, processing of encrypted signals seems like an oxymoron: once signals are encrypted the necessary information to do any meaningful processing is obscured. Fortunately this contradiction is only seemingly, and there is a growing community of researchers exploring and discovering new methods to manipulate encrypted signals. In March 2013, the IEEE Signal Processing Magazine brings you a special issue on signal processing in the encrypted domain (SPED). Among others, the need for SPED technologies originates from a growing societal awareness and relevance of security and privacy. Being able to process a plethora of sensitive signals at potentially untrusted sites, without or minimally leaking information, is one of the main motivators for SPED technologies. Core technologies that are being investigated in the SPED community include foundational principles, cryptographic techniques specifically tailored towards processing of fuzzy signals, or homomorphic encryption schemes, allowing the performance of algebraic operations on encrypted data. In this special issue, the editors and the authors aim to provide the reader with a broad overview of the state of the art in SPED, both for core technologies and applications. The interested readers can read the editorial article, and nice exciting research articles in the March issue of IEEE Signal Processing Magazine.